A Mutation in the Arabidopsis HYL1 Gene Encoding a dsRNA Binding Protein Affects Responses to Abscisic Acid, Auxin, and Cytokinin

Abstract

Both physiological and genetic evidence indicate interconnections among plant responses to different hormones. We describe a pleiotropic recessive Arabidopsis transposon insertion mutation, designated hyponastic leaves ( hyl1 ), that alters the plant's responses to several hormones. The mutant is characterized by shorter stature, delayed flowering, leaf hyponasty, reduced fertility, decreased rate of root growth, and an altered root gravitropic response. It also exhibits less sensitivity to auxin and cytokinin and hypersensitivity to abscisic acid (ABA). The auxin transport inhibitor 2,3,5-triiodobenzoic acid normalizes the mutant phenotype somewhat, whereas another auxin transport inhibitor, N -(1-naphthyl)phthalamic acid, exacerbates the phenotype. The gene, designated HYL1 , encodes a 419-amino acid protein that contains two double-stranded RNA (dsRNA) binding motifs, a nuclear localization motif, and a C-terminal repeat structure suggestive of a protein-protein interaction domain. We present evidence that the HYL1 gene is ABA-regulated and encodes a nuclear dsRNA binding protein. We hypothesize that the HYL1 protein is a regulatory protein functioning at the transcriptional or post-transcriptional level. INTRODUCTIONThe development, growth, and survival of plants under a wide range of environmental conditions reflect an intricate interplay of physical and chemical conditions with the highly integrated sensing and response networks in plants. The growth habit and physiological properties of plants can differ markedly under different regimes of light, gravity, temperature, humidity, and salinity, among others. Hormones have long been known to be important internal mediating signals in plants, but the components of the underlying cellular machinery are just beginning to be identified and characterized (Trewavas and Malho, 1997; Grill and Himmelbach, 1998;Solano and Ecker, 1998;D'Agostino and Kieber, 1999). The range of proteins involved in receiving, transmitting, and responding to external signals includes receptorlike and other kinds of protein kinases, phosphatases, and transcription factors, as well as enzymes such as thioredoxin and farnesyltransferase, which influence protein structure or localization through mechanisms other than phosphorylation (Mulligan et al., 1997; Becraft, 1998;Bonetta and McCourt, 1998; Hooley, 1998;Bleecker, 1999;Thornton et al., 1999; Hirt, 2000;Urao et al., 2000).Ample physiological evidence supports the presence of interconnections among plant responses to different environmental stimuli; moreover, evidence is accumulating that certain mutations can simultaneously influence the response to more than one hormone or altered physical parameter (Wilson et al., 1990;Clouse et al., 1996;Nemeth et al., 1998;Ephritikhine et al., 1999a; Beaudoin et al., 2000; Ghassemian et al., 2000). The implication is that individual proteins can be responsible for such interconnections, either transmitting multiple signals or participating in distinct complexes that transmit different signals (Elio...

Characterization of EMU, the Arabidopsis homolog of the yeast THO complex member HPR1

“…It was demonstrated that SE also functions in miRNA processing through interacting with HYL1, which acts solely in miRNA biogenesis (Lu and Fedoroff 2000;Han et al 2004;Vazquez et al 2004;Grigg et al 2005;Lobbes et al 2006;Yang et al 2006;Fang and Spector 2007;Dong et al 2008;Laubinger et al 2008). Although there is no evidence that the THO complex plays a direct role in miRNA processing in metazoa, the observed genetic interaction between emu and se-1 prompted us to further examine a potential role for EMU in miRNA biogenesis.…”

Posttranscriptional control of plant development

“…As the first three proteins have been the subjects of a previous review [40], we describe them only briefly. abh1, sad1, and hyl1 mutants all show hypersensitivity to ABA during seed germination, but hyl1 and sad1 mutants appear to have more pleiotropic phenotypes [41][42][43]. The HYL1 protein contains two dsRBDs [41].…”

“…abh1, sad1, and hyl1 mutants all show hypersensitivity to ABA during seed germination, but hyl1 and sad1 mutants appear to have more pleiotropic phenotypes [41][42][43]. The HYL1 protein contains two dsRBDs [41]. Both ABH1 and SAD1 appear to be the only Arabidopsis orthologs of subunits of basic RNA-processing machineries in yeast and metazoans [42,43].…”

A Peep into the Plant miRNA World

“…hyl1 affects leaf development, apical dominance and hor-mone sensitivity. It exhibits hyper-sensitivity to abscisic acid and hypo-sensitivity to cytokinin and auxin (Lu Plant Cell 2000) [57], (Vazquez Mol Cell 2004) [58]. Complete loss of HEN1 and HYL1 function causes phenotypes that are much less severe than those of ago1 or dcl1 mutants, indicating that HEN1 and HYL1 are redundant with other genes for miRNA biogenesis and function.…”